Use of Bitmap.GetPixel function to determine near-collision

[MetalMartian]

I'm trying to write code for a game based on the original Pacman in Visual Basic .NET 2003, however I can't figure out how to make the character move around the screen and not go through the walls. I've tried using a Collide function, however this means I would need to use several labels as the boundaries. This also means the two objects must intersect, so the user has to reverse out of the wall before continuing the game. I tried using the Bitmap.GetPixel function to determine the colours in a bitmap (resembling the original Pacman map) that I drew in Flash 8, and this has had limited achievement. Sometimes the character can move, other times it can't. I'm not entirely sure why. And then in certain areas it displays an error message saying

"Invalid parameter used.
System.ArgumentException: Invalid parameter used.
at System.Drawing.Bitmap.GetPixel(Int32 x, Int32 y)
at Learn_To_Spell_With_Munchie.frmMunchieGame.tmrGame _Tick(Object sender, EventArgs e) in E:\IPT\Semester 3\Assignments\Major Programming Assignment\Learn To Spell With Munchie\frmMunchieGame.vb:line 972
at System.Windows.Forms.Timer.OnTick(EventArgs e)
at System.Windows.Forms.Timer.DebuggableCallback(IntP tr hWnd, Int32 msg, IntPtr idEvent, IntPtr dwTime)"

The GetPixel part of my code is:

Private Sub tmrGame_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles tmrGame.Tick
        picMunchie.Left = picMunchie.Left + DeltaX
        picMunchie.Top = picMunchie.Top + DeltaY
        Dim Background As Bitmap = picGameArea.Image
        Dim TopPixel As Color = Background.GetPixel(picMunchie.Left + (picMunchie.Width / 2), picMunchie.Top - 1)
        Dim LeftPixel As Color = Background.GetPixel(picMunchie.Left - 1, picMunchie.Top + (picMunchie.Height / 2))
        Dim RightPixel As Color = Background.GetPixel(picMunchie.Left + picMunchie.Width + 1, picMunchie.Top + (picMunchie.Height / 2))
        Dim BottomPixel As Color = Background.GetPixel(picMunchie.Left + (picMunchie.Width / 2), picMunchie.Top + picMunchie.Height + 1)
        If TopPixel.ToArgb = -16776961 Or BottomPixel.ToArgb = -16776961 Or LeftPixel.ToArgb = -16776961 Or RightPixel.ToArgb = -16776961 Then
            DeltaX = 0
            DeltaY = 0
        End If
 

(N.B. picMunchie is the user's character they are moving around the screen)

If anyone could please give me some tips as to whether this is the right approach or not it would be much appreciated. Thanks.